package com.easytools.tools;

import java.util.Arrays;

/**
 * package: com.easytools.tools.Base64Utils
 * author: gyc
 * description:与Base64相关的工具类
 * time: create at 2017/1/2 0:26
 */

public class Base64Utils {

    private static final char[] CA =
            "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();
    private static final int[] IA = new int[256];

    private Base64Utils() {
        throw new UnsupportedOperationException("u can't instantiate me...");
    }

    static {
        Arrays.fill(IA, -1);//将指定的int值赋给指定的整数数组的每个元素
        for (int i = 0, iS = CA.length; i < iS; i++) {
            IA[CA[i]] = i;
        }
        IA['='] = 0;
    }

    private static final byte[] encodingTable = { (byte) 'A', (byte) 'B',
            (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F', (byte) 'G',
            (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L',
            (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P', (byte) 'Q',
            (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U', (byte) 'V',
            (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z', (byte) 'a',
            (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f',
            (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k',
            (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o', (byte) 'p',
            (byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u',
            (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y', (byte) 'z',
            (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4',
            (byte) '5', (byte) '6', (byte) '7', (byte) '8', (byte) '9',
            (byte) '+', (byte) '/' };
    private static final byte[] decodingTable;
    static {
        decodingTable = new byte[128];
        for (int i = 0; i < 128; i++) {
            decodingTable[i] = (byte) -1;
        }
        for (int i = 'A'; i <= 'Z'; i++) {
            decodingTable[i] = (byte) (i - 'A');
        }
        for (int i = 'a'; i <= 'z'; i++) {
            decodingTable[i] = (byte) (i - 'a' + 26);
        }
        for (int i = '0'; i <= '9'; i++) {
            decodingTable[i] = (byte) (i - '0' + 52);
        }
        decodingTable['+'] = 62;
        decodingTable['/'] = 63;
    }

    /**
     * 编码
     * @param data 原始数据
     * @return 编码后的数据
     */
    public static byte[] encode(byte[] data) {
        byte[] bytes;
        int modulus = data.length % 3;
        if (modulus == 0) {
            bytes = new byte[(4 * data.length) / 3];
        } else {
            bytes = new byte[4 * ((data.length / 3) + 1)];
        }
        int dataLength = (data.length - modulus);
        int a1;
        int a2;
        int a3;
        for (int i = 0, j = 0; i < dataLength; i += 3, j += 4) {
            a1 = data[i] & 0xff;
            a2 = data[i + 1] & 0xff;
            a3 = data[i + 2] & 0xff;
            bytes[j] = encodingTable[(a1 >>> 2) & 0x3f];
            bytes[j + 1] = encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3f];
            bytes[j + 2] = encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3f];
            bytes[j + 3] = encodingTable[a3 & 0x3f];
        }
        int b1;
        int b2;
        int b3;
        int d1;
        int d2;
        switch (modulus) {
            case 0: /* nothing left to do */
                break;
            case 1:
                d1 = data[data.length - 1] & 0xff;
                b1 = (d1 >>> 2) & 0x3f;
                b2 = (d1 << 4) & 0x3f;
                bytes[bytes.length - 4] = encodingTable[b1];
                bytes[bytes.length - 3] = encodingTable[b2];
                bytes[bytes.length - 2] = (byte) '=';
                bytes[bytes.length - 1] = (byte) '=';
                break;
            case 2:
                d1 = data[data.length - 2] & 0xff;
                d2 = data[data.length - 1] & 0xff;
                b1 = (d1 >>> 2) & 0x3f;
                b2 = ((d1 << 4) | (d2 >>> 4)) & 0x3f;
                b3 = (d2 << 2) & 0x3f;
                bytes[bytes.length - 4] = encodingTable[b1];
                bytes[bytes.length - 3] = encodingTable[b2];
                bytes[bytes.length - 2] = encodingTable[b3];
                bytes[bytes.length - 1] = (byte) '=';
                break;
        }
        return bytes;
    }

    /**
     * 解码
     * @param data 经过编码的数据
     * @return 原始数据
     */
    public static byte[] decode(byte[] data) {
        byte[] bytes;
        byte b1;
        byte b2;
        byte b3;
        byte b4;
        data = discardNonBase64Bytes(data);
        if (data[data.length - 2] == '=') {
            bytes = new byte[(((data.length / 4) - 1) * 3) + 1];
        } else if (data[data.length - 1] == '=') {
            bytes = new byte[(((data.length / 4) - 1) * 3) + 2];
        } else {
            bytes = new byte[((data.length / 4) * 3)];
        }
        for (int i = 0, j = 0; i < (data.length - 4); i += 4, j += 3) {
            b1 = decodingTable[data[i]];
            b2 = decodingTable[data[i + 1]];
            b3 = decodingTable[data[i + 2]];
            b4 = decodingTable[data[i + 3]];
            bytes[j] = (byte) ((b1 << 2) | (b2 >> 4));
            bytes[j + 1] = (byte) ((b2 << 4) | (b3 >> 2));
            bytes[j + 2] = (byte) ((b3 << 6) | b4);
        }
        if (data[data.length - 2] == '=') {
            b1 = decodingTable[data[data.length - 4]];
            b2 = decodingTable[data[data.length - 3]];
            bytes[bytes.length - 1] = (byte) ((b1 << 2) | (b2 >> 4));
        } else if (data[data.length - 1] == '=') {
            b1 = decodingTable[data[data.length - 4]];
            b2 = decodingTable[data[data.length - 3]];
            b3 = decodingTable[data[data.length - 2]];
            bytes[bytes.length - 2] = (byte) ((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 1] = (byte) ((b2 << 4) | (b3 >> 2));
        } else {
            b1 = decodingTable[data[data.length - 4]];
            b2 = decodingTable[data[data.length - 3]];
            b3 = decodingTable[data[data.length - 2]];
            b4 = decodingTable[data[data.length - 1]];
            bytes[bytes.length - 3] = (byte) ((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 2] = (byte) ((b2 << 4) | (b3 >> 2));
            bytes[bytes.length - 1] = (byte) ((b3 << 6) | b4);
        }
        return bytes;
    }

    /**
     * 解码
     * @param data 经过编码的数据
     * @return 原始数据
     */
    public static byte[] decode(String data) {
        byte[] bytes;
        byte b1;
        byte b2;
        byte b3;
        byte b4;
        data = discardNonBase64Chars(data);
        if (data.charAt(data.length() - 2) == '=') {
            bytes = new byte[(((data.length() / 4) - 1) * 3) + 1];
        } else if (data.charAt(data.length() - 1) == '=') {
            bytes = new byte[(((data.length() / 4) - 1) * 3) + 2];
        } else {
            bytes = new byte[((data.length() / 4) * 3)];
        }
        for (int i = 0, j = 0; i < (data.length() - 4); i += 4, j += 3) {
            b1 = decodingTable[data.charAt(i)];
            b2 = decodingTable[data.charAt(i + 1)];
            b3 = decodingTable[data.charAt(i + 2)];
            b4 = decodingTable[data.charAt(i + 3)];
            bytes[j] = (byte) ((b1 << 2) | (b2 >> 4));
            bytes[j + 1] = (byte) ((b2 << 4) | (b3 >> 2));
            bytes[j + 2] = (byte) ((b3 << 6) | b4);
        }
        if (data.charAt(data.length() - 2) == '=') {
            b1 = decodingTable[data.charAt(data.length() - 4)];
            b2 = decodingTable[data.charAt(data.length() - 3)];
            bytes[bytes.length - 1] = (byte) ((b1 << 2) | (b2 >> 4));
        } else if (data.charAt(data.length() - 1) == '=') {
            b1 = decodingTable[data.charAt(data.length() - 4)];
            b2 = decodingTable[data.charAt(data.length() - 3)];
            b3 = decodingTable[data.charAt(data.length() - 2)];
            bytes[bytes.length - 2] = (byte) ((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 1] = (byte) ((b2 << 4) | (b3 >> 2));
        } else {
            b1 = decodingTable[data.charAt(data.length() - 4)];
            b2 = decodingTable[data.charAt(data.length() - 3)];
            b3 = decodingTable[data.charAt(data.length() - 2)];
            b4 = decodingTable[data.charAt(data.length() - 1)];
            bytes[bytes.length - 3] = (byte) ((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 2] = (byte) ((b2 << 4) | (b3 >> 2));
            bytes[bytes.length - 1] = (byte) ((b3 << 6) | b4);
        }
        return bytes;
    }

    /**
     * 解码
     * @param data 经过编码的数据
     * @return 原始数据
     */
    public static String decode2String(String data) {
        return new String(decode(data));
    }

    private static byte[] discardNonBase64Bytes(byte[] data) {
        byte[] temp = new byte[data.length];
        int bytesCopied = 0;
        for (int i = 0; i < data.length; i++) {
            if (isValidBase64Byte(data[i])) {
                temp[bytesCopied++] = data[i];
            }
        }
        byte[] newData = new byte[bytesCopied];
        System.arraycopy(temp, 0, newData, 0, bytesCopied);
        return newData;
    }

    private static String discardNonBase64Chars(String data) {
        StringBuffer sb = new StringBuffer();
        int length = data.length();
        for (int i = 0; i < length; i++) {
            if (isValidBase64Byte((byte) (data.charAt(i)))) {
                sb.append(data.charAt(i));
            }
        }
        return sb.toString();
    }

    private static boolean isValidBase64Byte(byte b) {
        if (b == '=') {
            return true;
        } else if ((b < 0) || (b >= 128)) {
            return false;
        } else if (decodingTable[b] == -1) {
            return false;
        }
        return true;
    }

    /** Encodes a raw byte array into a BASE64 <code>String</code> representation i accordance with RFC 2045.
     * @param sArr 待转换字节数组The bytes to convert. If <code>null</code> or length 0 an empty array will be returned.
     * @param lineSep 是否使用分隔符 Optional "\r\n" after 76 characters, unless end of file.<br>
     * No line separator will be in breach of RFC 2045 which specifies max 76 per line but will be a
     * little faster.
     * @return A BASE64 encoded array. Never <code>null</code>.
     */
    public final static String encodeToString(byte[] sArr, boolean lineSep)
    {
        // Reuse char[] since we can't create a String incrementally anyway and StringBuffer/Builder would be slower.
        return new String(encodeToChar(sArr, lineSep));
    }

    /** Encodes a raw byte array into a BASE64 <code>char[]</code> representation i accordance with RFC 2045.
     * @param sArr The bytes to convert. If <code>null</code> or length 0 an empty array will be returned.
     * @param lineSep Optional "\r\n" after 76 characters, unless end of file.<br>
     * No line separator will be in breach of RFC 2045 which specifies max 76 per line but will be a
     * little faster.
     * @return A BASE64 encoded array. Never <code>null</code>.
     */
    public final static char[] encodeToChar(byte[] sArr, boolean lineSep)
    {
        // Check special case
        int sLen = sArr != null ? sArr.length : 0;
        if (sLen == 0)
            return new char[0];

        int eLen = (sLen / 3) * 3;              // Length of even 24-bits.
        int cCnt = ((sLen - 1) / 3 + 1) << 2;   // Returned character count
        int dLen = cCnt + (lineSep ? (cCnt - 1) / 76 << 1 : 0); // Length of returned array
        char[] dArr = new char[dLen];

        // Encode even 24-bits
        for (int s = 0, d = 0, cc = 0; s < eLen;) {
            // Copy next three bytes into lower 24 bits of int, paying attension to sign.
            int i = (sArr[s++] & 0xff) << 16 | (sArr[s++] & 0xff) << 8 | (sArr[s++] & 0xff);

            // Encode the int into four chars
            dArr[d++] = CA[(i >>> 18) & 0x3f];
            dArr[d++] = CA[(i >>> 12) & 0x3f];
            dArr[d++] = CA[(i >>> 6) & 0x3f];
            dArr[d++] = CA[i & 0x3f];

            // Add optional line separator
            if (lineSep && ++cc == 19 && d < dLen - 2) {
                dArr[d++] = '\r';
                dArr[d++] = '\n';
                cc = 0;
            }
        }

        // Pad and encode last bits if source isn't even 24 bits.
        int left = sLen - eLen; // 0 - 2.
        if (left > 0) {
            // Prepare the int
            int i = ((sArr[eLen] & 0xff) << 10) | (left == 2 ? ((sArr[sLen - 1] & 0xff) << 2) : 0);

            // Set last four chars
            dArr[dLen - 4] = CA[i >> 12];
            dArr[dLen - 3] = CA[(i >>> 6) & 0x3f];
            dArr[dLen - 2] = left == 2 ? CA[i & 0x3f] : '=';
            dArr[dLen - 1] = '=';
        }
        return dArr;
    }
}
